1. Field of the Invention
The present invention relates to bituminous roofing products such as asphalt-based roofing membranes and processes for making such roofing products.
2. Brief Description of the Prior Art
Asphalt-based roofing membranes are excellent waterproofing materials that have been extensively used in low-slope roofing systems to provide long-lasting and satisfactory roof coverings. Low-slope roofing systems are extensively used for commercial and industrial buildings. Examples of low-slope roofing systems are built-up roofs (BUR), modified bitumen roofs, and single-ply or membrane roofing systems. Asphalt-based roofing membranes are frequently used as waterproofing underlayment in low-rise roofing systems, as well as the uppermost or finish layer in built-up-roofs. Built-up roofs are sometimes covered with a layer of gravel or granular mineral material to protect the roofing membrane against mechanical damage.
Mineral-surfaced asphalt shingles, such as those described in ASTM D225 or D3462, are generally used for steep-sloped roofs to provide water-shedding function while adding aesthetically pleasing appearance to the roofs. Conversely, roll goods such as asphalt-based roofing membranes are generally used for low-slope roofs. Pigment-coated mineral particles are commonly used as color granules in roofing applications to provide aesthetic as well as protective functions. Roofing granules are generally used in asphalt shingles or in roofing membranes to protect asphalt from harmful ultraviolet radiation.
Roofing products such as asphalt shingles and roll stock are typically composite articles including a non-woven glass fiber or felt web covered with a coating of water repellent bituminous material, and optionally surfaced with protective mineral-based roofing granules. The bituminous material is characteristically black in color, and is strongly absorptive of incident solar radiation. Thus, asphalt-based roofing membranes can absorb significant amounts of solar radiation, which can result in elevated roof temperatures. This can contribute to the increase of energy usage for indoor air-conditioning, especially in a hot climate.
Asphalt shingles are generally constructed from asphalt-saturated roofing felts and surfaced by pigmented color granules. Asphalt-based roofing membranes are similarly constructed; except that roofing granules are not frequently employed. However, both asphalt shingles and asphalt-based roofing membranes are known to have low solar reflectivity and hence will absorb solar heat especially through the near infrared range of the solar spectrum.
This phenomenon increases as the surface becomes dark in color. For example, white-colored asphalt shingles with CIE L* greater than 60 can have solar reflectance greater than 25% (ASTM E1918 method), whereas non-white asphalt shingles with L* less than 60 can have solar reflectance in the range of 5-20%. As a result, it is common to measure temperatures as high as 71-77 degrees C. (160-170 degrees F.) on the surface of dark roofing shingles on a sunny day with 27 degree C. (80 degrees F.) ambient temperature.
Reduced energy consumption is an important national goal. For example, the State of California has a code requirement that all commercial roofing materials in low-slope applications need to exceed a minimum of 70% solar reflectance in order to meet California's energy budget code. Also, in order to qualify as Energy Star® roofing material, a roofing membrane needs to exceed 65% solar reflectance.
Typically, even a white mineral-surfaced, asphalt-based roofing membrane has only 30-35% solar reflectance.
In order to address this problem, externally applied coatings have sometimes been applied directly onto the shingle or membrane surface on the roof. White pigment-containing latex coatings have been proposed. Similarly, aluminum-coated asphalt roofing membranes have been employed to achieve solar heat reflectivity. U.S. Pat. No. 6,245,850 discloses a reflective asphalt emulsion for producing a reflective asphalt roofing membrane.
The use of exterior-grade coatings colored by infrared-reflective pigments has also been proposed for spraying onto the roof in the field. U.S. Patent Application Publication No. 2003/0068469A1 discloses an asphalt-based roofing material comprising a mat saturated with asphalt coating and a top coating having a top surface layer that has a solar reflectance of at least 70%.
U.S. Patent Application Publication No. 2002/0160151A1 discloses an integrated granule product comprising a film having a plurality of ceramic-coated granules bonded to the film by a cured adhesive and the cured adhesive or the film can have pigments. Such integrated granule product can be directly bonded to an asphalt-based substrate as roofing products.
In order to increase solar reflectance of built-up roofs, reflective coatings have been applied directly onto the surface of the roofing membrane. For example, white pigment containing latex coatings have been proposed and evaluated by various manufacturers. In addition, white single-ply roofing membranes formed from thermoplastic elastomers, PVC, or EPDM, etc., have been developed to achieve the required solar reflectance. Performance Roof Systems (Kansas City, Mo.) has also developed an asphalt-based roofing membrane having a white acrylic pre-impregnated mat on the top surface.
Laminated single-ply roofing membranes are known, such as those disclosed in U.S. Pat. Nos. 6,502,360; 5,456,785; 5,620,554; and 5,643,399. U.S. Pat. No. 6,296,912 discloses a roofing membrane having a fibrous layer on top for providing a secure surface for roof installation personnel.
There is a continuing need for roofing materials that have improved resistance to thermal stresses while providing an attractive appearance. Further, there is a continuing need to develop asphalt-based roofing membranes with solar reflectance greater than 70%.